Method of producing all skin rayon



United States Patent Ofifice Edd-$444 Patented Oct. 8, 1963 This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose frornviscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, wood pulp, mixtures thereof, and the hitch first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon dis-ulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to Washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after these treatments.

The filaments as formed by the conventional methods consist of a skin or outer shell portion ad a core portion with a sharp line of demarcation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalent metal salts are present in the spinning bath. The skin and core portions of the filament represent differences in structure and these different portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff. t

It has now been discovered that the presence of small amounts of certain alkali-soluble alkylene oxide adducts of N-fatty alkyl propylene diamin'e in viscose results in the production of shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the adduct is maintained within certain limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as compared to convenhigher alkyl amines.

' oils.

tional filaments include a smooth, non-crenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of compounds which may be termed N-fatty alkyl-N-(omega-hydro-xy polyoxyalkylene)-N-di(omega-hydroxy polyoxyalkylene) propylene diamines as represented by the formula R (C n ZnO) y NCH2CH2CH2N H (CnHinO) x (Cn En 111 where R is a straight hydrocarbon or fatty alkyl chain of from 8 to 18 carbon atoms, n is 2 or 3, x, y and z are Whole numbers and the sum of x, y and z is from about 10 to about or more, preferably between about 15 and about 50.

These compounds may be derived from primary fatty The amine may be relatively pure such as capryl, lauryl, stearyl, methyl, ethyl or butyl amine. Alternatively, there may also be used commercially available fatty alkyl amines which are derived from animal and vegetable fats and oils 'such as coconut oil, cottonseed oil, corn oil, soya bean oil, palm oils, peanut oil, tallow and the like and the hydrogenated fats and Such fatty alkyl amines consist of a mixture of amines of the long straight hydrocarbon chains or fatty alkyl chains of the fatty acids obtained from the particular fat or oil, the chains having the same number of carbon atoms as the fatty acids in which they have their origin. Thus, a fatty amine or fatty alkyl amine derived from coconut oil, for example, will consist of a mixture of fatty amines wherein the individual amines have fatty alkyl radicals of from,8 to '18 carbon atoms with the individual amines in a distribution corresponding to the distribution of the fatty acids of coconut oil. For this specific fatty alkyl amine, lauryl amine would constitute about 50% of the mixture.

The N-fatty alkyl phopylene diamine is reacted with an ralky'lene oxide; for example, ethylene oxide or propylene oxide to form an alkylene oxide adduct of the diamin'e. It is possible that the adducts may have byd-roxy polyoxyalkylene chains of different lengths replacing each of the amino hydrogen atoms and that the alkylene oxide units are not in all cases equally distributed in the adducts. Theoretically, an adduct containing an average of 15 alkylene oxide units per molecule of the diarnine would correspond to the foregoing formula wherein each of x, y and z is 5. The adducts must have sufficient alkali-solubility to be dissolved in the viscose. The adduct may be conveniently added to the viscose in the form of a solution in alkali or water. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water and alkali solutions such as a 6% caustic solution, the ethylene oxide adducts are preferred. Accordingly, the invention will be illustrated by reference to the ethylene oxide adducts.

The amount of the adduct which is incorporated in viscose must be at least about 3% by weight of the cellulose in the viscose and may vary up to about 5%, preferably, the amount varies from 3.5% to 4.5%. Lesser amouuts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products.

Amounts within the preferred range are most effective in enhancing the characteristics and properties of the products. The adduct may be added at any desired stage in the productionof the viscose such as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while it is being dissolved in the caustic solution or to the viscose solution before or 3 after filtration. The adduct or modifier prcfera ly is added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

i re viscose may contain from about 4% to about cellulose, the particular source of the cellulose being selected for the ultimate use of the regenerated cellulose product. The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose containing the small amount of the adduct, may have a sodium chloride stlt test above about 8 and preferably above about 9 at the time of spinning or extrusion.

In order to obtain the improvements enumerated hereinbefore, it is essential that the composition of the spinning bath be maintained within a well defined range. The presence of the adduct in the viscose combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity, high abrasion resistanw, high fatigue resistance and consisting of filaments composed entirely of skin.

Generically and in terms of the industrial art, the ning bath is a lo-u acid-high zinc spinning bat-h. The bath should contain from about 10% to about 25% sodium sulfate and from about 3% to about zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 (3., preferably be ween about C. to about 70 C. As is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about C. and C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is suificiently rapid to form a filament having a skin and core. There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is :sufficiently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing the adduct lies between about 5% and about 8.5%. The acid concentration may be increased as the amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of additive or modifier and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the adduct is increased beyond about 5% while other conditions are maintained constant. Lesser amounts of sulfuric acid may be employed. Greater amounts of sulfuric acid result in the reduction of products having skin and core. A lowering of the amount of modifier, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. The maximum concentration of acid WllOll is permissible for the production of all ssiin products is about 9%.

The presence of the adducts in the viscose retards the coagulation and, therefore, the amount of modifier e rzloyed must be reduced at high spinning speeds. hus, for optimum physical characteristics of an all skin yarn formed from a viscose as above and at a spinning peed of about 50 meters per minute, the modifier is employed in amounts within the lower portion of the range, for example, about 3.5%. The determination of the specific maximum and optimum concentration of acid for any specific viscose, spinning bath and spinning speed is a matter of simple experimentation for those skilled in the art. The extruded viscose must, of course, be immersed or maintained in the spinning bath for a period sufficient to effect relatively complete coa ulation of the viscose, that is, the coagulation must be sulficient so that the filaments will not adhere to each other as they are brought together and withdrawn from the bath.

in the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. It is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been completed.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the adducts and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed to the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments from a viscose containing about 7.4% cellulose, about 6.6% caustic soda, and having a total carbon disulfide content of about 36%. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2 /2 hours. The cellulose xanthate was then dissolved in caustic soda solution. The adduct was added to the caustic soda solution and mixed for about /2 hour. The viscose was then allowed to ripen for about 30 hours at 18 C. The adduct was a mixture of compounds corresponding to the foregoing formula wherein the fatty alkyl groups of the compounds were derived from tallow and the ethylene oxide content was an average of about 15 units per molecule of propylene diamine.

The viscose was extruded through a spinneret to form a 205 to 210 denier, 100 filament yarn at a rate as set forth in the table which follows. The coagulating and regenerating bath was maintained at a temperature of about 60 C. The yarn was passed over a godet from which it was conducted through a hot Water bath maintained at about 95 C. During the travel through the hot water bath, the yarn was stretched an amount as set forth in the table. The yarn was then collected in a spinning box, washed free of acid and salts and dried.

The specific spinning conditions and the physical properties of the yarns are set forth in the following table:

7 swelling amounting to from about 45% Example I II III IV Viscose:

Percent Adduet 4 0 4 Salt Test 8.7 9. 2 8. 4 8.8

ath:

Percent H2804 7. 4 7. 4 8. 7 8. 7

Percent 7111804.. 6 6 6 6 Percent Na sOi 16 16 16 16 Spin Speed. 22 22 36 36 Percent Stretch 83 83 -76 76 T. d!y 3. 2 2.8 2.8 2.7 '1. wet" 2. 4 2.0 1.9 1.9 E. dry- 19 19 17 18 E. we 26 25 23 22 Percent Skin 100 65 100 60 NOTE .-Spin speed-Speed of extrusion of viscose in meters per minute. T. dry and T. wetTensile strength of dry and wet yarn, respectively, in grams per denier. r E.1 dry and E. wetPer'cent elongation of dry and wet yarn, respeclVE Y. i

The individual filaments formed in accordance with this invention (Examples I and III) have a smooth, noncrenulated exterior surface and consist entirely of skin,

no core being detectable at high magnification (e.g.

1500 The individual filaments of the control yarns (Examples 11 and IV) formed from the same viscose solution without the addition of the modifier and spun under substantially identical conditions exhibit a very irregular and serrated surface and consist of about 60% to about 65% skin and the balance core with a sharp line of demarcation between the skin and core.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the ease and simplicity with which such properties may be determined. In some instances, products made in aceordance with this invention might not exhibit improvements in tenacity and elongation, however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinabove.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65 to about 80% for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the to about 60%. If desired, small amounts of the adducts may be added to the spinning bath. Since the adducts are water-soluble, some of the modifier will be leached from the filament and will be present in the bath.

The modifier of this invention may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The adducts or modifiers may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinning.

' The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently.

stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS cone. (General Dyestuffs Corp.) for l to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and d-ioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a division of my copending application Serial No. 550,852, filed December 5, 1955, entitled Methodof Producing All Skin A'ayon.

While preferred embodiments of the invention have been disclosed, the description is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing a small amount of a modifier into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%, the modifier corresponding to the formula N-OHrCHsOHr-N H(OnH-. n0) 1 (011112110) 111 wherein R is a fatty alkyl hydrocarbon chain having between 8 and 1-8 carbon atoms, n is a whole number at least 2 butnot greater than 3, x, y and z are wholenumbers and the sum of 'x, y and z is between about 10 and about 100, said small amount of the modifying agent being a quantity s-ufiicient to impart a smooth, non-crenulated surf-ace and a substantially all skin structure to products formed by spinning the viscose at a sodium chloride salt test of at 'least 9 into an aqueous bath containing from 15% to 2 2% sodium sulfate, from 4% to 9% zinc sulfate and sulfuric acid in an amount not exceeding 9%, but the quantity being insufficient to adversely affect the physical properties of such products.

2. The step in the method as defined in claim 1 wherein the modifier corresponds to a formula as defined in claim 1 in which n is 2.

3. The step in the method as defined in claim 1 wherein the modifier is a mixture of compounds corresponding to the formula as defined in claim 1 and in which the fatty alkyl hydrocarbon chains (R) are derived from the fatty acids of natural fats and oils and n is -2.

4. In a method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin, the step which comprises extruding viscose containing from about 3% to about 5%, based on the weight of the '2' cellulose in the viscose, of a modifier into an aqueous spinning bath containing from about to 25% sodium sulfate, from about 3% to zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%, the modifier corresponding to the formula R (Cn 2nO)L'n NCH2OH2CH2N H c nmno) n (C nHalo) .11 wherein R is a fatty alkyl hydrocarbon chain having be tween 8 and 18 carbon atoms, 11 is a whole number at least 2 but not greater than 3, x, y and z are whole numbers and the sum of x, y and z is between about 10 and about 100.

5. The step in the method as defined in claim 4 wherein the modifier corresponds to a formula as defined in claim 4 in which n is 2.

6. The step in the method as defined in claim 4 wherein the modifier is a mixture of compounds corresponding to the formula as defined in claim 4 and in which the fatty a-lkyl hydrocarbon chains (R) are derived from the fatty acids of natural fats and oils and n is 2.

7. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in viscose from about 3.5% to about 4.5%, based on the weight of the cellulose in the viscose, of a modifier and extruding the viscose into an aqueous spinning bath containing from about 10% to 25% sodium sulfate, from about 3% to 15% zinc sulfate and sulfuric acid, the sulfuric acid content of the bath exceeding the slubbing point but not exceeding about 9%, the modifier corresponding to the formula R (cnmnomr \NCH2CH2CI1'2N II(CnIIZnO) x (011112110) 1H wherein R is a fatty alkyl hydrocarbon chain having between 8 and 18 carbon atoms, 12 is a whole number at least 2 but not greater than 3, x, y and z are Whole numbers and the sum of x, y and z is between about 10 and about 100.

8. The method as defined in claim 7 wherein the modifier is a mixture of compounds corresponding to the formula as defined in claim 7 and in which the fatty alliyil hydrocarbon chains (R) are derived from the fatty acids of natural fats and oils and n is 2.

9. The method of producing shaped bodies of regenerated cellulose consisting substantially entirely of skin which comprises adding to and incorporating in a viscose from about 3.5% to about 4.5%, based on the weight of the cellulose in the viscose, the viscose containing about 7.4% cellulose, about 6.6% caustic soda and about 36% carbon disulfide, based upon the weight of the cellulose, ripening the viscose to a salt point of not lower than about 8 and extruding the viscose into an aqueous spinning bath containing from about 16% to 20% sodium sulfate, from about 4% to 9% zinc sulfate and sulfuric acid, the sulfuric acid content of the spinning bath exceeding the slubbing point but not exceeding about 9%, the modifier corresponding to the formula R (o nHMO) II N-CHzCH2CHz-N H(C l.Hzno) x (0 .1112.0) ,II wherein R is a fatty alkyl hydrocarbon chain having between 8 and 18 carbon atoms, 12 is a whole number at least 2 but not greater than 3, x, y and z are whole numbers and the sum of x, y and z is between about 10 and about 100.

10. The method as defined in claim 9 wherein the modifier is a mixture of compounds corresponding to the formula as defined in claim 9 and in which the fatty alkyl hydrocarbon chains (R) are derived from the fatty acids of natural fats and oils and n is 2.

References Cited in the file of this patent UNITED STATES PATENTS 2,593,4 o MacLaurin et 'al Apr. 22, 1952 2 852,3 4 Hollihan et al Sept. 16, 1953 FOREIGN PATENTS 213,643 Australia Apr. 18, 1957 

1. IN A METHOD OF PRODUCING SHAPED BODIES OF REGENERATED CELLULOSE CONSISTING SUBSTANTIALLY ENTIRELY OF SKIN, THE STEP WHICH COMPRISES EXTRUDING VISCOSE CONTAINING A SMALL AMOUNT OF A MODIFIER INTO AN AQUEOUS SPINNING BATH CONTAINING FROM ABOUT 10% TO 25% SODIUM SULFATE, FROM ABOUT 3% TO 15% ZINC SULFATE AND SULFURIC ACID, THE SULFURIC ACID CONTENT OF THE SPINNING BATH EXCEEDING THE SLUBBING POINT BUT NOT EXCEEDING ABOUT 9%, THE MODIFIER CORRESPONDING TO THE FORMULA 